Balance

Balance disorders are among the most frequent impairments of individuals who have sustained a brain injury. The rehabilitation of balance is a major goal for interventions because balance and postural control are crucial in most daily activities.

In 1986, Horak and Nashner postulated that the balance behavior, however complex it may be, consists of a limited repertoire of central motor programs. They identified three different movement synergies, known as the ankle, the hip, and the stepping strategy, which are executed continuously with the common objective of stance, but with different mechanisms. While the goal of the ankle and hip strategies is to maintain the center of pressure within the base of support, the stepping strategy aims to expand the base of support in such a way it includes the center of pressure.

Leaving aside the controversy of these findings, in a series of experiments we have investigated the effect of training these strategies through virtual reality-based interventions in the balance condition after a brain injury.

Ankle and hip strategy

Systems based on force platforms are particularly interesting, since they enable to estimate the weight distribution of the patients by means of pressure sensors. In contrast to laboratory-grade systems, the Wii Balance Board (Nintendo®, Kyoto, Japan), a peripheral of the Wii gaming system, is an inexpensive interface (less than $100) that has widespread availability. The Wii Balance Board also has the advantage of being portable, easy, and comfortable to handle thanks to its small size (0.511 m wide by 0.316 m long by 0.053 m thick) and weight (3.5 kg without batteries). Furthermore, it is a device with Bluetooth wireless connectivity that is battery operated. The Wii Balance Board contains four force sensors (located in each corner) that are used to measure the user’s center of balance and weight. Users can interact with the game by means of weight transferences.

Although their hardware features are very interesting, the Wii Balance Board videogames are oriented to the entertainment of healthy population, and may require motor and cognitive skills that individuals with acquired brain injury may lack. To overcome this limitation, we designed different exercises that promoted the training of the ankle and hip strategies. Exercises provided audiovisual information of the center of pressure and required participants to displace it towards different targets in the virtual environment through weight transferences and postural readjustments.

The efficacy of the training of the ankle and hip strategies was initially tested in randomized controlled trial on a sample of chronic hemiparetic individuals with acquired brain injury.1 Participants underwent a physical therapy program or combined physical therapy with customized exercises using the Wii Balance Board. After an intensive intervention, participants in the experimental group significantly improved their balance condition compared to patients who underwent traditional therapy. In addition, participants reported the experienced as enjoyable and motivational.

These results were replicated in a longitudinal study on a stroke sample, which also proved that the improvements were maintained one month after the intervention.2

Stepping strategy

With regards to the stepping strategy, in order to estimate the participants’ feet movements we used different tracking solutions along time, as an optical solution using OptiTrack V100:R2 cameras (NaturalPoint, Corvallis, OR, USA) with two reflective markers, the electromagnetic G4 with two sensors (Polhemus, Colchester, VT, USA), or the Kinect or Kinect v2 (Microsoft, Redmond, WA, USA), which enable human pose recognition from depth images and provides the 3D position of many body joints without any wearable device. It is important to highlight that subjective perceptions and preferences are far from being constant among different populations, thus suggesting that these considerations, together with the performance parameters, should be also taken into account when designing a rehabilitation system.3

To train the stepping strategy we designed an exercise that immersed the participants in a 3D virtual environment, where their feet were represented by two shoes that mimicked their movement in the real world. Initially, both shoes appeared in the center of the virtual environment inside a circle, around which some items rose from the ground. The objective of the task was to reach the items with the nearer foot while maintaining the other foot within the circle. A third-person view, which allowed the participants to see the virtual items all around them, was used.

A preliminary study involving individuals with acquired brain injury and optical tracking showed that the training of the stepping strategy could provide benefits to the balance condition.4 Interestingly, a setting using the novel skeleton-based tracking devices, as the Kinect, was shown to provide similar effects.5

A randomized controlled trial involving chronic hemiparetic stroke survivors and a very similar design evidenced greater improvement in balance in the experimental group when compared to the control group.6 Again, participants’ feedback was very positive. The training of the stepping exercise could have improved the speed and precision of the supporting base changes and one-leg standing ability, which are important abilities for many daily activities, such as walking (one-leg support phase).

The novel Kinect-based technology allows motion tracking at a low cost in such a way that these devices can be used for in-home rehabilitation. In a randomized controlled trial we examined whether an intervention with these devices can be effective and save costs.7 Our results evidenced that virtual reality-based telerehabilitation interventions can promote the reacquisition of locomotor skills associated with balance in a similar way that in-clinic interventions, both complemented with a conventional therapy program. In addition the usability and the motivation of both interventions can be similar. And finally, the telerehabilitation interventions can involve savings that vary depending on each particular scenario.

Assessment

Posturography systems that incorporate force platforms are considered to assess balance and postural control with greater sensitivity and objectivity than conventional clinical tests. The Wii Balance Board has been shown to have similar performance characteristics as other force platforms, but with lower cost and size. We have designed a web-based tool that allows clinicians to carry out posturographic assessments using the Wii Balance Board.8 Benefits of this tool are that it is freely available to the public and that results can be shared among sites. The system can be acessed here or from the Resources accessed area in our website.

Healthy individuals and individuals with stroke participated in the study. Both groups were assessed using the Wii Balance Board-based posturography system. Individuals with stroke were also assessed using a laboratory grade posturography system and a battery of clinical tests to determine the concurrent validity of the system. A group of subjects were assessed twice with the Wii Balance Board-based system to determine its reliability. Concurrent validity with another posturography system was moderate to high. Correlations with clinical scales were consistent with previous research. The reliability of the system was excellent in almost all measures. In addition, the system successfully characterized individuals with stroke with respect to the healthy population.

The Wii Balance Board-based posturography system exhibited excellent psychometric properties and sensitivity for identifying balance performance of individuals with stroke in comparison with healthy subjects, which supports feasibility of the system as a clinical tool.